This invention relates generally to offset lithography and more particularly to a disposable combination master/blanket sheet for use in the process.
In an offset lithographic duplicating press of the conventional type, there is provided master, blanket and impression cylinders all mounted for rotation. The master and impression cylinders are positioned for contacting engagement with the blanket cylinder. An imaged master sheet is attached by means of a mechanical clamp of the like device to the outer surface of the master cylinder. Ink applied to the master is received in the oleophilic imaged areas. As the master and blanket cylinders rotate, the inked image is transferred to the surface of the blanket cylinder. Conventionally, the blanket cylinder is covered with a rubber or the like ink receptive (oleophilic) material known as the blanket.
Paper fed between the blanket and impression cylinders receives the inked image from the blanket to complete the printing process.
After the completion of a run wherein a predetermined number of copies are printed, the master sheet is discarded. This can be accomplished manually or in some cases automatically. Also, the blanket must be washed every time a master is discarded to remove any ink remaining thereon. This is normally accomplished by the application of a solvent. In the latter case, the operation of the duplicating press must be discontinued while the clean-up process takes place. Also, the clean-up process can become messy.
In an attempt to minimize the need for cleaning up the blanket and to reduce the "down time" of the duplicating press, it has been suggested to provide a disposable blanket consisting of a foam plastic sheet or paper sheet having a rubber or rubber-like coating thereover. This sheet is mounted on the blanket cylinder similarly to the attachment of a sheet to the master cylinder and upon completion of a copy run is discarded along with the master.
While the provision of the disposable blanket simplifies somewhat the duplicating process by eliminating the need for a solvent wash, it has the disadvantage that at the conclusion of each printing run, both a master and blanket sheet must be discarded. This can become costly. Furthermore, it becomes necessary to purchase and store both master and blanket sheets to carry out the process.